1. Field of the Invention
The present invention relates to a micro-mirror device for an image display apparatus which can change the traveling path of incident light by pivoting a mirror that is installed to correspond to each pixel and, more particularly, to a micro-mirror device for an image display apparatus and method which can increase optical efficiency by pivoting a mirror in the direction of the sides of the mirror.
2. Description of the Related Art
In general micro-mirror devices for an image display apparatus include a plurality of mirrors that are installed to be driven by an electrostatic force to reflect incident light at a predetermined angle. These micro-mirror devices are used in image display devices of projection televisions, and optical scanning devices such as scanners, photocopying machines, and facsimiles. In particular, when these micro-mirror devices are used in image display devices, the number of mirrors equals the number of pixels arranged two-dimensionally, and each of the mirrors is driven in response to an image signal for a corresponding pixel, thus reflected light has varying paths of travel resulting in the formation of a picture.
Referring to FIG. 1, a conventional micro-mirror device 1 for an image display apparatus includes a substrate 10, a pair of first posts 20 formed on the substrate 10, an electrode 15 formed on the substrate 10, a girder or support assembly 30, and a second post 40 which protrudes from the girder 30. The device also includes a mirror 50 supported by the second post 40, which changes a reflection angle of incident light upon its upper surface according to an inclination angle that is determined by electrostatic attraction. The pair of first posts 20, which support the girder 30, protrude vertically from the substrate 10 by a predetermined amount and are isolated a predetermined distance apart from each other. The electrode 15 includes a pair of base electrodes 11 installed on the substrate 10, which are isolated a predetermined distance apart from each other, and connection electrodes 13, which are formed on the substrate 10 so as to contact one end of each of the first posts 20, and apply current to the mirror 50. The girder 30 is pivoted on portions that are supported by the pair of first posts 20. The girder 30 is made up of a horizontal supporter 31 for supporting the second post 40, and a pair of springs 33 that, respectively, connect the pair of first posts 20 to both ends of the horizontal supporter 31. The pair of springs 33, which are elastically deformed by mutual electrostatic attraction between the mirror 50 and the base electrode 11, are rotated in opposite directions as the electrostatic attraction is created. Thus, the horizontal supporter 31 is pivoted, so that the mirror 50 is slanted vertically. In the micro-mirror device having such a structure, the base electrodes 11 are arranged on a diagonal line on the substrate 10, so that the mirror 50 pivots on a diagonal line, which forms a 45° angle with respect to the horizontal direction of the mirror 50.
When the micro-mirror device having the above-described structure is adopted in an image display apparatus, a plurality of micro-mirror devices are arranged in two-dimensional array structure, as shown in FIG. 2. The micro-mirror devices, arranged as described above, are driven around a rotating axis positioned on a diagonal line, resulting in shapes of the micro-mirror devices being projected as shown in FIG. 3, when viewed from a side of a light source that emits illuminating light to the micro-mirror devices 1. Specifically, FIG. 3 illustrates the shapes of the micro-mirror devices that are projected when light from the light source is converged at 10° angles and illuminated to the diagonally-driven micro-mirror devices 1 for an image display apparatus which pivots at ±10° angles, that is, which has a tilt angle of 20°. Compared to a tilt angle of 0° when parallel light beams are incident, the diagonally-driven micro-mirror device 1 has an optical efficiency of about 91%, which is obtained by taking the product of the cosine of the tilt angle and the square of the cosine of the convergence angle, i.e., cos(tilt angle)×cos2(convergence angle)=cos 20°×cos2(20°). Thus, an optical loss of about 9% is generated.